Ultraviolet light has a degradative effect on olefin polymers; the severity of this effect is dependent on the particular polymer and the geographical location of exposure. The degradation may take the form of discoloration, loss of tensile and impact strength, distortion of initial flexibility, dimensional change, surface craze, cracking, powdering or increased electrical conductivity. All of these effects may result from the breaking of carbon-to-carbon bonds in the polymer chain followed by immediate oxidation of the chain fragments.
It is well known that the addition of certain materials to an olefin polymer will impart a degree of stabilization to that polymer with respect to its resistance to the destructive function as preferential acceptors of incident ultraviolet radiation because they have a much higher affinity for such radiation than does the olefin polymer. It appears that they absorb harmful radiation and dissipate it as harmless energy. They thus form a protective shield for the polymer in which they are present.
The need for stability to exposure to ultraviolet light is apparent. Any olefin polymer composition which is to be used in the outdoor atmosphere, i.e., exposed to sunlight, will suffer the deteriorating influence of ultraviolet radiation and must be capable of withstanding that deterioration.
Stability toward excessive heat is also required of olefin polymer compositions. The mere act of mixing polymer compositions and then fabricating them into usable shapes invariably requires the use of high temperatures and it is obviously important that the polymer composition remain substantially unchanged throughout any such treatment.
Chiddix et al. (U.S. Pat. No. 3,763,287) show antioxidant compounds having the structure ##STR2## WHERE R and R' are alkyl, aralkyl or cycloalkyl; m is 1-4; X is alkyl, aryl, aralkyl, cycloalkyl, alkylphenoxy, thioalkyl, thiophenyl, haloalkyl, or alkylcarboxyl; and n is 1-3. Also shown are the corresponding phosphates and thiophosphates. These compounds are said to be useful as antioxidants in a wide variety of organic compounds normally susceptible to oxidation, including plastics, elastomers, synthetic lubricants, hydraulic fluids, hydrocarbon lubricants, fuels, fats, oils, etc.
Chiddix et al. (U.K. Pat. No. 1,355,109) show somewhat similar compounds where the P-X.sub.3-n is replaced by COR, R being an n valent organic radical such as alkyl or cycloalkyl.
Dexter et al. (U.S. Pat. No. 3,285,855) show esters of hindered hydroxyphenylalkanoic acids having the structure ##STR3## where R and R' are lower alkyl, x is 0-6 and y is 6-30. These esters likewise are said to be effective antioxidants in a wide variety of organic materials normally susceptible to oxidation. Dexter et al. (U.S. Pat. No. 3,330,859) show substantially the same thing. Dexter et al. (U.S. Pat. No. 3,644,842) show much the same except that the alcohol portion of the ester is derived from a glycol, viz., neopentylglycol, glycerin, ethylene glycol, propylene glycol, 1,18-octadecanediol, pentaerythritol, etc.
Hechenbleikner et al. (U.S. Pat. No. 3,839,506) show certain phosphonates having the structure ##STR4## where n is 1-4 and R and R' can be alkyl of 1-20 carbon atoms.
The invention of this application is a substituted nitriloacetate having the structure ##STR5## where R and R' are lower alkyl radicals and n is 1-4. Preferably, they are tertiary alkyl radicals and, in the usual instance, they are the same. In the usual case, n is 3. The nitriloacetates may be prepared by transesterification of trimethyl nitriloacetate with a 3(3,5-dialkyl-4-hydroxyphenyl) propanol, as follows: ##STR6## The use of a molecular sieve to accept the methanol as it is formed in the reaction is helpful. The tris-3(3,5-ditertiarybutyl-4-hydroxyphenyl)propyl nitriloacetate which is prepared by such a process is a pale yellow crystalline solid melting at 108.degree.-110.degree. C.
R and R' are as indicated lower alkyl radicals, i.e., they each contain 1-8 carbon atoms. Preferably they are tertiary alkyl radicals and, usually, they are alike. Tertiary butyl radicals are especially preferred.
The above-substituted nitriloacetates impart significant heat and light stability to olefin polymer compositions in which they are present.
Typical preparation of the substituted nitriloacetates herein are shown in the following examples.